1. Field of the Invention
The present invention relates to a temperature control device which regulates the temperature of a battery pack mounted in a vehicle.
2. Description of Related Art
A battery temperature control device for regulating the temperature of a battery pack mounted in a vehicle is disclosed in Published Japanese Patent First Publication No. 2004-1674. In this device, to prevent the temperature of the battery pack from being excessively heightened, the temperature of air is regulated in an air control unit, and the temperature-controlled air (hereinafter, called controlled air) is led from the control unit to the battery pack through a duct to regulate the temperature of the battery pack. Therefore, the control unit can prevent the temperature of the battery pack from being excessively heightened, so that the battery pack is not degraded.
In contrast, when the temperature of the battery pack is excessively lowered, it is required to raise the temperature of the battery pack for the purpose of preventing the output of the battery pack from being lowered. Because vehicles having water-cooled engines are usually used, a cooling water of the engine is heated by the heat generated in the engine, and the control unit produces hot air by using the heat of the hot cooling water. Therefore, when the hot air is blown against the battery pack, the temperature of the battery pack can be increased.
However, the rate of heat transfer required to warm up the battery pack is approximately five times higher than that required to cool the battery pack. Therefore, as compared with a case where the warmed battery pack is cooled down, when the hot air is blown against the battery pack, the rate of heat transfer to the battery pack is insufficient to warm up the pack. Therefore, it takes a long time to warm up the excessively cooled battery pack, or it is difficult to sufficiently warm up the cooled battery pack to a desired temperature. Especially, when the driving operation of the cooled engine is started on condition that the temperature of cooling water of the engine is considerably lowered, it takes a long time to produce hot air in the control unit. Therefore, it is difficult to quickly or reliably raise the temperature of the battery pack.
Further, the thermal diffusion from ends of the battery pack to the vehicle compartment is larger than that from the center of the battery pack. When the battery pack is gradually warmed up, a temperature difference inevitably occurs in the battery pack. Therefore, it is difficult to uniformly warm the whole battery pack.
Moreover, there is an idea that the charging and discharging operations are repeatedly performed in the battery pack to generate the heat in the battery pack by using the internal resistance of the pack. However, although the battery pack can be quickly and uniformly warmed up, the electric power of the battery pack is used only for warming the pack. Therefore, fuel consumption is undesirably increased so as to deteriorate fuel economy of the vehicle.